GCodeWidget Improvements

Summary:

• Do not add open files to m_openFiles
• Reload openfiles instead of opening a new copy
  • Do not start with "new File" . User can't save it and can not print it unless saved
  • Allow for closing of files in the gcode editor
  • track the tab / documents to keep view current (needs more work ?)

Test Plan:
Open Documents, Close documents.
Try to open the same document hopefully get pushed to its tab..

Reviewers: patrickelectric, laysrodrigues, tcanabrava

Reviewed By: patrickelectric, laysrodrigues, tcanabrava

Subscribers: cullmann, Atelier: General Development

Tags: Atelier: General Development

Differential Revision: https://phabricator.kde.org/D12690